Material for four directional reinforcement of conical shaped object, method for fabricating same and object formed therewith

ABSTRACT

Radially extending fibers are disposed over a conical surface at predetermined sites. The sites correspond to vertices of a pattern of contiguous congruent isosceles triangles inscribed onto the surface of a sector of a circle which may be conformally mapped onto the conical surface so that vertices of the pattern coincide along the join line meridian of the conical surface. Fibers are disposed between the radially extending fibers in three different directions which respectively correspond with the sides of the triangles. The material obtained exhibits an invariant fiber volume fraction along the axis of the conical surface. The material may be used to reinforce a conical object. Also, an object, such as a preform, having a conical surface and method for reinforcing an object having a conical surface, in accordance with the present invention, are described.

BACKGROUND OF THE INVENTION

This invention relates to a four directional (4D) material and methodfor reinforcing a conical shaped object with fiber elements and to aconical preform formed from fiber elements, wherein the fiber volumefraction along the axis and circumference of the conical surface remainsinvariant.

In certain applications wherein an object is expected to be exposed to arelatively harsh environment, typically a composite material is used toform the object or to be applied to surfaces of the object forprotection against the environment and/or for reinforcing the object. Itis desirable that the composite material have a substantially constantfiber element reinforcement fraction over the surface of the object sothat significant composite property disparities between areas of thesurface are avoided, thereby permitting accurate predictions ofcomposite material response to the environment. It has been especiallydifficult to obtain a constant fiber reinforcement fraction along theaxis of a conical or other axially increasing diameter shell structure.Further, the resulting reinforcement material should not exhibitdiscontinuities or a seam along the join line or other portion of theconical surface.

Prior three-dimensional fiber reinforcement patterns have drawbacks whenconfigured to form or conform to a conical surface. These includefailing to maintain constant radial and in-plane (i.e. over the conicalsurface) fiber reinforcement fractions along the length of the conicalsurface while maintaing continuous paths for winding the in-plane fibersthrough a radially disposed fiber array; or failing to providecontinuous paths for winding the in-plane portion of the fiberreinforcement material while maintaining a lower variation of radial andin-plane fiber volume fractions along the length of the conical surface.For the former case, which is typical of three-directional polarreinforcement designs, significant variations in structural propertiesoccur along the length of the conical surface since the radial andin-plane fiber reinforcement fractions vary with axial position alongthe conical surface. In the latter case, discontinuities in the in-planefiber reinforcement paths result in structural deficiencies and makefabrication of a fiber reinforcement preform impractical.

U.S. Pat. No. 4,519,290--Inman et al discloses a three-dimensional 4Dbraided preform fabrication for making annular or conical sections to beused in producing articles. The 4D fiber architecture includes aplurality of rods of carbon fibers uniformly distributed over thesurface and inserted into a conical mandrel perpendicular to the conicalcenterline as shown in FIG. 2 of the patent. Oblique carbon or graphitefibers are then passed alternately over and under similar longitudinalfibers around the radially extending rods to provide a triaxial braidedpattern having a repeating unit cell that is illustrated in FIG. 6 ofthe patent. However, the 4D fiber architecture described in U.S. Pat.No. 4,519,290 does not achieve invariance of fiber volume fraction alongthe conical surface.

Another 4D configuration is described in U.S. Pat. No. 4,400,421--Stover, wherein the four directions of groups of reinforcing fibersremain parallel to repeating elements of the group. Although a similarunit cell to that employed in the present invention is obtained, amethod for deploying or conformally mapping a planar array onto aconical surface to obtain constant fiber volume without discontinuitiesor a seam at the join line is not described or illustrated.

A 4D triangular fiber arrangement is described in a DTIC reportADBO49350 entitled "Boron Nitride--Boron Nitride Composite Material" byPotter and Place. FIG. 4 of the Potter and Place report illustrates acylindrical configuration having three triangularly related fibersdisposed in a plane perpendicular to the axis of the cylinder and onefiber disposed in a plane parallel to the axis of the cylinder. Thisfiber arrangement would not generate a constant fiber volume fraction ofradial fibers over a conical shell, nor would a constant fiber volumefraction be obtained in the conical surface direction of the shellwithout addition of new fiber ends.

U.S. Pat. No. 4,570,166--Kuhn et al, describes conformal mapping of aplanar sector of a circle, having a grid pattern of isosceles trianglesinscribed therein, onto the surface of a cone corresponding to thesector in the context of an RF transparent conically shaped antennashield structure. The vertices of the triangles are used to situate RFcomponents in the antenna shield structure.

Accordingly, it is an object of the present invention to provide amethod for forming a three dimensional fibrous element preform for aconical object, wherein the preform includes an invariant fiber volumefraction along the axis and circumferential direction of the object.

Another object is to provide a material fabricated from fiber elementsthat may be configured in a conical shape and have an invariant fibervolume fraction along the axis of the conical shape.

Yet another object is to provide a method for reinforcing an objecthaving a conical surface, wherein a single fiber element may be used toform the in-plane fraction while obtaining invariant fiber fractionalong the axis.

Still another object is to provide a conical shaped preform or materialfor reinforcing a conical surface wherein there is no seam along thejoin line or other area of the conical portion and further whereindiscontinuities throughout the conical portion are avoided.

SUMMARY OF THE INVENTION

In accordance with the present invention, a material for reinforcing aconical surface includes three elements, the second overlaying thefirst, the third overlaying the second and each skewedly disposed withrespect to each other such that when conformed to the conical surfacethe elements intersect in a plan view of the conical surface withincontiguous congruent isosceles triangles. Respective ones of a pluralityof fourth elements are disposed at the vertices of the triangles so thatthe first, second and third elements are disposed between respectivepredetermined ones of the plurality of fourth elements and the fourthelements are further disposed to be substantially perpendicular toproximate portions of each of the first, second and third elements. Thefirst, second and third elements are conformable to the conical surfaceand respective ones of the plurality of fourth elements are disposablesubstantially perpendicular to a respective localized portion of theconical surface for reinforcing the conical surface.

In another aspect of the present invention, a preform includes first,second and third elements configured for defining a conical surface. Thesecond element overlays the first element and the third element overlaysthe second. Each element is skewedly disposed to the others such thatthe first, second and third elements intersect in a plan view of theconical surface within continguous congruent isosceles triangle.Respective ones of a plurality of fourth elements are disposed at thevertices of the triangles and are further disposed to be substantiallyperpendicular to proximate portions of each of the other elements and toa respective localized portion of the conical surface.

In yet other aspects of the present invention, a method for reinforcingan object having a conical surface and a method for forming a triaxialfilament winding having a conical surface and a constant fiber volumefraction over the conical surface with no seams are described.

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself, however,both as to organization and method of operation, together with furtherobjects and advantages thereof, may best be understood by reference tothe detailed description taken in connection with the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1A and 1B show radial reinforcement patterns for respectivesurface winding patterns on a conical surface wherein nonuniform fiberreinforcement fractions are obtained.

FIG. 2A shows a sector of a circle having a triangular grid patterninscribed thereon that may be formed to define a conical surface inaccordance with the present invention.

FIG. 2B shows the sector of FIG. 1 formed into a cone and theorientation of a unit cell at the join line meridian of the cone inaccordance with the present invention.

FIG. 3 is an enlarged view of the area around the intersection of theradii of the sector along line 3--3 of FIG. 2A.

FIG. 4 is an enlarged partial view of the area around the intersectionof a radius and the arc of the circle of the sector of FIG. 2A from theviewpoint of line 4--4 of FIG. 2A.

FIG. 5 illustrates a representative portion of a fiber element weavingpattern including a unit cell in accordance with the present invention.

FIG. 6 is a representative perspective view of a portion of the materialformed when woven in accordance with the pattern of FIG. 5.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B, a frustum 100 of a cone 110 is shownhaving a grid pattern 105 for locating radially (with respect to centralaxis 125, which may be an axis of revolution of cone 110) extendingfibers from the conical surface of frustum 100. For a predeterminedconstant number of equally circumferentially spaced grid members of gridpattern 105 that are disposed in a circumferential row of grid 105 andfor a predetermined equal axial spacing between adjacent circumferentialrows of grid members of grid 105, the arcuate circumferential spacingbetween adjacent members of a row increases for each respective row thatis closer to larger base 104 of frustum 100. Thus the radial fiberreinforcement fraction monotonically decreases from smaller base 102 tolarger base 104 of frustum 100.

As shown in FIG. 1B, an additional grid pattern 115 is disposed over thelower portion of the conical surface of frustum 100 so that a meridionalcolumn of grid pattern 115 is situated between adjacent meridionalcolumns of grid pattern 105. Thus grid pattern 115 doubles the number ofgrid elements for the portion of the surface of frustum 100 over whichit is disposed. Placement of grid pattern 115 may be selected so thatthe arcuate circumferential spacing between members of grid 105 and grid115 toward smaller base 102 of furstum 100 is approximately equal to thearcuate circumferential spacing between members of grid 105 at smallerbase 102 of frustum 100. Grid 115 is shown starting at about themidpoint between base 102 and 104 and extending toward base 104.

Although the addition of grid pattern 115 to grid pattern 105 doesproduce a fiber reinforcement fraction along the axis of frustum 100that is more uniform between bases 102 and 104 as compared to theconfiguration shown in FIG. 1A, the fiber reinforcement fraction isstill not constant along the entire axis. Further, the resulting overallgrid pattern as illustrated in FIG. 1B, does not readily allow weavingby a single fiber element over the conical surface.

Referring to FIGS. 2A and 2B, a planar sector 10 is defined by radii 12and 14 and circumferential arc 16 of a circle and includes a gridpattern 18 disposed therein in accordance with the present invention.Grid pattern 18 is formed from a plurality of contiguous congruentisosceles triangles, one of which is designated triangle 50.

Sector 10 may be formed into a cone 20, wherein radii 12 and 14 coincidealong the join, or jam, line 21 of cone 20. Axis 25 coincides with anequivalent axis of rotation of an appropriately dimensioned trianglesuitable for forming cone 20 as an object of revolution. When gridpattern 18 is configured in accordance with the present invention ashereinafter described, grid pattern 18 may be exactly conformally mappedonto the surface of cone 20, so that triangles of grid 18 that includeone side formed by a portion of radius 12 or 14, such as triangles 11and 13, abut and exactly coincide along join line 21 to have a commonside and a pair of common vertices. The vertices of the triangles ofgrid pattern 18 are used to locate sites for radially extending fiberelements to be disposed on the conical surface in accordance with thepresent invention. The vertices of triangles 11 and 13 also define a"unit cell" that may be repeated over the conical surface of cone 20 toform grid 18.

The trigonometric relationship between the planar angle θ (FIG. 3)formed by the intersection of radii 12 and 14 of sector 10 and the halfangle α of cone 20 is:

    θ(degrees)=360°. (sinα)

Referring to FIG. 3, an enlarged view looking in the direction of thearrows of line 3--3 of FIG. 2A is shown. The apex of triangle 50coincides with vertex 15 (which is also the center of the circle) ofsector 10. Sides 51 and 53, which coincide with radii 12 and 14,respectively, terminate at vertices 52 and 54, respectively, of triangle50. Vertices 52 and 54 are predeterminedly selected so that side 51 isequal to side 53, whereby triangle 50 is isoscles, and equilateral ifapex angle θ equals 60°.

Sides 51 and 53 of triangle 50 are extended through vertices 52 and 54,respectively, a distance equal to sides 51 and 53 to terminate atvertices 62 and 64, respectively. A vertex 66 is designated at themid-point between vertices 62 and 64 along line 65 connecting vertices62 and 64. By connecting vertex 66 to vertex 52 with line 63 and tovertex 54 with line 67, it may be observed that triangles 70, 72 and 74,all of which are congruent to triangle 50, are formed. As is readilyapparent to one skilled in the art, the process of extending sides oftriangles and determining vertices for locating radial fibers that areultimately to be disposed over the conical surface of cone 20 (FIG. 2B)may be repeated until the entire surface of sector 10 (FIG. 2A) iscovered. It is of course not necessary that the lines representing thesides of triangles actually be drawn, but only that the vertices of thetriangles be appropriately located. Further, the vertices may bedirectly located on the conical surface of cone 20 (FIG. 2B) withoutresort to sector 10(FIG. 2A). In addition, it is also to be understoodthat although the arrangement of grid pattern 18 (FIG. 2A) has beendescribed as it applies to a cone, the grid pattern may also be appliedby one of ordinary skill in the art using the teachings provided hereinto a frustum of a cone for obtaining the benefits of the presentinvention.

As a further aid to understanding the present invention, externalvertices 52, 54, 62, and 64 of triangles 70, 72 and 74 may be consideredthe vertices of a trapezoid having sides 61 and 69 and bases 55 and 65.The smaller base 55 of the trapezoid coincides with the base 55 oftriangle 50. By extension, another trapezoid having a smaller base 65that coincides with the larger base of the trapezoid defined by vertices52, 54, 62 and 64, a larger base 76 and vertices 62, 64, 71 and 77 maybe added. Additional vertices 73 and 75 are disposed on base 76 todivide base 76 into equal segments, thereby forming vertices oftriangles which are congruent to triangle 50. Thus each successivecontiguous trapezoid that is added to sector 10 as grid pattern 18progresses from apex 15 toward arc 16 of sector 10 is formed by addingone more vertex along the larger base of the trapezoid being added thanthe number of vertices in the larger base of the trapezoid next closerto apex 15, thereby adding two more triangles that are congruent totriangle 50. The geometrical element that is added to each successivetrapezoid to form the next trapezoid includes two triangles, one erectand the other inverted, that are both congruent to triangle 50. Thevertices of the two triangles that are added define a parallelogram thatis equivalent in plan view to the unit cell as defined by triangles 11and 13 in FIG. 2B.

Referring to FIG. 4, an enlarged view looking in the direction of thearrows of line 4--4 of FIG. 2A is shown. At intersection 17 of arc 16with radius 12, a portion of triangle 80 of grid pattern 18 lies outsidesector 10 and the number of vertices and whole triangles included withinsector 10 decreases from the previous row closer apex 15 (FIG. 2A).Successive ones of contiguous trapezoids that are added toward arc 16 toform grid 18 will extend beyond arc 16 of sector 10. However, theuniform triangular spacing and area density of the vertices remainingwithin sector 10 remains constant.

Referring to FIG. 5, an enlarged representative portion of the conicalsurface of cone 20 includes a portion of the four directional weavingpattern of the present invention disposed thereon. Radially extendingelements R are disposed at the vertices of triangles in accordance withpattern 18 of congruent isosceles triangles as hereinbefore describedand are further disposed to be perpendicular to the respective localportion of the conical surface of cone 20 at the respective vertex. Forsmall cone half angles radially extending elements R may be disposedsubstantially perpendicular to axis 25 (FIG. 2B) if desired. Elements U,V and W follow and conform to the surface contour of cone 20 so thatelements U, V and W are locally each perpendicular to proximate elementsR. Elements R are shown with a hexagonal cross-section forcorrespondence of the boundaries of elements R with the boundaries ofelements U, V and W. Of course, elements R are not so limited and mayinclude any cross-sectional shape consistent with obtaining the desiredperformance. Although elements R, U, V and W may each comprise a singlefiber, in a generally preferred embodiment, as shown more clearly inFIG. 6, elements R, U, V and W each respectively include a plurality offibers.

Element W is shown wrapped in a horizontal direction (i.e. parallel tothe base defined by arc 16 of sector 10 (FIG. 2B)) and disposed betweenpredetermined ones of elements R. Element V is wrapped over element W atan angle A with respect to element W which generally corresponds to abase angle of a triangle of grid 18 and element U is wrapped overelement V at an angle B with respect to element W which generallycorresponds to a base angle of a triangle of grid 18. Elements U and Vare each disposed between appropriate predetermined ones of elements R.When thus wrapped or woven on the conical surface of cone 20, elementsU, V and W form a triangular surface wrap pattern which in combinationwith elements R form a four directional reinforcement design. Further,elements U, V and W are parallel to corresponding proximate sides of thetriangles of grid 18.

It should be understood that the relative orientation between trianglesdefined by grid pattern 18 and the apex or base of cone 20 does notremain constant but rotates along a circumferential path. Thus, forcertain applications it may be preferable for grid 18 to includeequilateral or nearly equilateral triangles, since for isoscelestriangles wherein the bases are significantly greater than or less thanthe sides of the triangles, undesirable effects, such as in plane fibercurvature discontinuities at the join line, may be experienced whenattempting to weave a layer of an in-plane element. This change inrelative orientation of the triangles of grid 18 will also effect theorientation of elements U, V and W with respect to cone 20. For example,element W as shown in FIG. 5 will not remain horizontal to the base ofcone 20 but will spiral, i.e. change axial position, as itcircumferentially traverses the conical surface of cone 20. Elements Uand V will also spiral so that the same relative position betweenelements U, V and W is maintained. When thus wrapped or woven on theconical surface of cone 20, elements U, V and W form a triangularsurface wrap pattern which in combination with elements R form a fourdirectional reinforcement design.

A plan view of elements U, V and W shows that elements U, V and W aredisposed with respect to each other at angles which are respectivelyequal to the angles of the triangles of grid 18. The angle at whichelements U and V are wrapped with respect to element W may not beexactly equal to angle θ since a change may occur when grid 18 or sector10 is conformally mapped onto the conical surface of cone 20 due to thecurvature of the conical surface and the curvilinear orientation ofelements U, V and W for conforming to the conical surface.

In one method of practicing the invention, elements R are disposed atvertices of isosceles triangles and substantially perpendicular to arespective local portion of the conical surface of cone 20. A completelayer of element W is wrapped using a continuous fiber, or roving, overthe conical surface of the cone to a predetermined thickness with arotating angular placement or spiral effect to cover the adjacent pathsbetween predetermined ones of elements R. The wrapped layer of element Wis then overlaid with a complete layer of element V, preferably using anuninterrupted extension of the same fiber that wrapped element W, overthe conical surface of the cone to a predetermined thickness with arotating angular placement to cover the paths between elements R thatare skewedly, obliquely or slantingly disposed with respect to elementW. The wrapped layer of element V is then overlaid with a complete layerof element U, preferably using an uninterrupted extension of the samefiber that wrapped elements W and V, over the conical surface of thecone to a predetermined thickness with a rotating angular placement tocover the paths between elements R that are skewedly, obliquely orslantingly disposed with respect to elements W and V. The wrapped layerof element U may then be overlaid with layers following the orientationand sequence of elements W, V and U until a desired predeterminedthickness for the overall fabric or weave is obtained. In order toincrease efficiency and speed in wrapping elements U, V and W with acontinuous fiber, it may be desirable to place a mandrel beyond the apexand base of cone 20 so that the fiber can be conveniently turned aroundthe mandrel to start the next pass over the surface of the cone. Aftercompletion of winding the appropriate number of elements U, V and W toachieve the desired depth and at least partial densification, the fiberextending beyond the apex and base of the cone may be trimmed.

Thus a reinforcement fabric or "preform" may be wound on a conicalsurface wherein at any predetermined depth into the fabric the fabrichas a constant fiber volume fraction along the axis and circumference ofthe cone. Due to divergence of the radially disposed elements, the fibervolume fraction in the radial direction decreases as the distance fromthe surface of the cone increases.

Previous schemes for attempting to reduce and/or eliminate fiber volumefraction variation along the axis of conically woven structures havechanged the size of the fibers used for weaving each direction and/orvaried the number of fiber ends along the axis. In the present inventionthe same sized elements may be used for all radial elements R and eachof the conical surface elements U, V and W may be equal to each otherwhile obtaining the benefits of the present invention. Further, theradial and surface elements may be equal to each other. In addition, asingle fiber weaving end can be used when forming the surface elements,which can therefore be developed without loose or extra end insertionfor obtaining axial fiber fraction invariance.

The resulting woven fabric material, or web, may be densified byconventional techniques that are compatible with elements R, U, V and Win order to form a composite material. Although the composition of thefiber for forming the elements R, U, V and W of the weave is generallynot critical for obtaining the benefits of the present invention,exemplary fibers may comprise fused silica or carbon with thedensification means or ingredients used for densifying comprising silicaand carbon, respectively.

The description above has included a cone for supporting the elements R,U, V and W to be disposed thereon and/or to be reinforced by elements R,U, V and W. However, the invention is not so limited. Elements R, U, Vand W may be combined in a conical shape in accordance with theteachings herein without resort to a cone, or the cone may be removedeither after weaving or after the resulting woven net material has beendensified for forming a conical shaped billet having an interior conicalshaped void. Further, the present invention may be practiced using afrustum of a cone.

In certain application, it may be desirable to form a triaxial filamentwinding that conforms to a conical surface. Such a winding may beachieved in accordance with the present invention by weaving surfacefibers U, V and W, without resort to radial fibers R and then densifyingthe resulting material.

Also, there may be an occasion when it would be desirable that thevertices of the isoceles triangles on the surface of the cone areidentified, elements U, V and W are woven between respectivepredetermined ones of the identified vertices and then the radialelements R are disposed at the identified vertices. The presentinvention contemplates such processing.

Thus has been illustrated and described a method for forming a threedimensional fibrous preform for a conical object, wherein the preformincludes an invariant fiber volume fraction along the axis of theobject. Further, a material fabricated from fibers that may beconfigured in a conical shape and have an invariant fiber volumefraction along the axis of the shape has been shown and described. Also,a method for reinforcing an object having a conical surface has beenillustrated and described.

While only certain preferred features of the invention have been shownby way of illustration, many modifications and changes will occur tothose skilled in the art. It is to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit and scope of the invention.

What is claimed is:
 1. A material for reinforcing a conical surface,comprising:a plurality of first fiber elements, a respective one of theplurality of first fiber elements disposed at a respective vertex of aplurality of contiguous congruent isosceles triangles; and second, thirdand fourth fiber elements, the third fiber element overlaying the secondfiber element, the fourth fiber element overlaying the third fiberelement, and the second, third and fourth fiber elements skewedlydisposed with respect to each other and the second, third and fourthfiber elements further disposed between predetermined vertices of theplurality of triangles such that the second, third and fourth fiberelements intersect within a predetermined triangle of the plurality oftriangles, wherein the second, third and fourth fiber elements areconformable to the conical surface such that the fiber volume fractionof the second, third and fourth fiber elements along the axis andcircumference of the conical surface is invariant, and the respectiveone of the plurality of first fiber elements disposed substantiallyperpendicular to a respective localized portion of the conical surfacewhen the second, third and fourth fiber elements are conformed to theconical surface.
 2. The material as in claim 1, wherein said isoscelestriangles are also equilateral.
 3. The material as in claim 1, whereinthe second, third and fourth fiber elements form a continuous member. 4.The material as in claim 2, wherein the second, third and fourth fiberelements form a continuous member.
 5. The material as in claim 1,further including densification means coupled to the first, second,third and fourth fiber elements for densifying the material.
 6. Apreform comprising:A plurality of first fiber elements, a respective oneof the plurality of first fiber elements disposed at respective verticesof contiguous congruent isosceles triangles; and second, third andfourth fiber elements configured for defining a conical surface, thethird fiber element overlaying the second fiber element and the fourthfiber element overlaying the third fiber element and the second, thirdand fourth fiber elements skewedly disposed with respect to each otherand the second, third and fourth fiber elements further disposed betweenpredetermined vertices of the plurality of trangles, such that thesecond, third and fourth fiber elements intersect within a predeterminedtriangle of the plurality of triangles, wherein each of the plurality offirst fiber elements is disposed substantially perpendicular to arespective localized portion of the conical surface and further disposedsubstantially perpendicular to each of the proximate portions of thesecond, third and fourth fiber elements, such that the fiber volumefraction of the second, third and fourth fiber elements along the axisand circumference of the conical surface is invariant.
 7. The preform asin claim 6, wherein said isosceles triangles are also equilateral. 8.The preform as in claim 6, wherein the second, third and fourth fiberelements form a continuous member.
 9. The preform as in claim 8, furtherincluding densification means coupled to the first, second, third andfourth fiber elements for densifying the preform.